Add item for page 235

docs/errata/README.md

@@ -4,7 +4,7 @@ If you find any mistakes in the seventh edition, *C# 11 and .NET 7 - Modern Cros
 
 [**Errata** (42 items)](errata.md): Typos, tool user interface changes, or mistakes in code that would cause a compilation error that prevents a successful build.
 
-[**Improvements** (29 items)](improvements.md): Changes to text or code that would improve the content. These are optional.
+[**Improvements** (30 items)](improvements.md): Changes to text or code that would improve the content. These are optional.
 
 [**Common Errors** (3 items)](common-errors.md): These are some of the most common errors that a reader might encounter when trying to get code in book tasks to work, or when trying to write your own code. 
 

docs/errata/improvements.md

@@ -1,4 +1,4 @@
-**Improvements** (29 items)
+**Improvements** (30 items)
 
 If you have suggestions for improvements, then please [raise an issue in this repository](https://github.com/markjprice/cs11dotnet7/issues) or email me at markjprice (at) gmail.com.
 
@@ -11,6 +11,7 @@ If you have suggestions for improvements, then please [raise an issue in this re
 - [Page 161 - Using lambdas in function implementations](#page-161---using-lambdas-in-function-implementations)
 - [Page 179 - Reviewing project packages](#page-179---reviewing-project-packages)
 - [Page 200 - Talking about OOP](#page-200---talking-about-oop)
+- [Page 235 - More about methods](#page-235---more-about-methods)
 - [Page 237 - Implementing functionality using methods](#page-237---implementing-functionality-using-methods)
 - [Page 241 - Defining flight passengers](#page-241---defining-flight-passengers)
 - [Page 251 - Setting up a class library and console application](#page-251---setting-up-a-class-library-and-console-application)
@@ -235,6 +236,129 @@ interface ITheta { void M3() { } void M4(); }
 class Iota : ITheta { void M4() { } }
 ```
 
+# Page 235 - More about methods
+
+> Thanks to [cgwid](https://github.com/cgwid) for raising this [issue on 12 April 2023](https://github.com/markjprice/cs11dotnet7/issues/59).
+
+In this section, we define some methods and operators so that two `Person` objects can get married and have babies. The example we model comes from the Bible story of Lamech and his two wives and their children. But the code I tell you to write does not allow Lamech to marry two women so later an exception is thrown when Lamech and his second wife try to make a baby. 
+
+cgwid suggested a solution in [the issue they raised](https://github.com/markjprice/cs11dotnet7/issues/59). 
+
+Here is my possible improvement. I might change it before using it in the next edition. We could use a `List<Person>` to store the zero, one or more people that a `Person` is married too. We could implement `Married` as a readonly property that calls the LINQ `Any` method to return `true` if there are any items in the `Spouses` list, as shown in the following code:
+```cs
+// Is this person married to anyone?
+public bool Married => Spouses.Any();
+
+// Allow multiple spouses.
+public List<Person> Spouses = new();
+```
+
+Then we can implement the `static Marry` method by checking if the person is already in the list and then adding them if they are not, as shown in the following code:
+```cs
+// static method to marry
+public static void Marry(Person p1, Person p2)
+{
+  if (p1.Spouses.Contains(p2) || p2.Spouses.Contains(p1))
+  {
+    throw new ArgumentException(
+      string.Format("{0} is already married to {1}.",
+      arg0: p1.Name, arg1: p2.Name));
+  }
+  else
+  {
+    p1.Spouses.Add(p2);
+    p2.Spouses.Add(p1);
+  }
+}
+
+// instance method to marry
+public void Marry(Person partner)
+{
+  Marry(this, partner);
+}
+```
+
+For convenience, we could create a method to output the number of and names of spouses of the current person, as shown in the following code:
+```cs
+public void OutputSpouses()
+{
+  if (Married)
+  {
+    string term = Spouses.Count == 1 ? "person" : "people";
+    WriteLine($"{Name} is married to {Spouses.Count} {term}:");
+    foreach (Person spouse in Spouses)
+    {
+      WriteLine($"  {spouse.Name}");
+    }
+  }
+  else
+  {
+    WriteLine($"{Name} is not married.");
+  }
+}
+```
+
+We would also need to change the `Procreate` method to check that the two people are married before allowing them to make a baby, as shown in the following code:
+```cs
+// static method to "multiply"
+public static Person Procreate(Person p1, Person p2)
+{
+  if (!p1.Spouses.Contains(p2))
+  {
+    throw new ArgumentException(
+      string.Format("{0} must be married to {1} to procreate with them.",
+      arg0: p1.Name, arg1: p2.Name));
+  }
+
+  Person baby = new()
+  {
+    Name = $"Baby of {p1.Name} and {p2.Name}",
+    DateOfBirth = DateTime.Now
+  };
+
+  p1.Children.Add(baby);
+  p2.Children.Add(baby);
+
+  return baby;
+}
+```
+
+Finally, we can call the `OutputSpouses` method in `Program.cs`, as shown in the following code:
+```cs
+// Implementing functionality using methods
+Person lamech = new() { Name = "Lamech" };
+Person adah = new() { Name = "Adah" };
+Person zillah = new() { Name = "Zillah" };
+
+lamech.Marry(adah);
+// Person.Marry(zillah, lamech);
+
+if (zillah + lamech)
+{
+  WriteLine($"{zillah.Name} and {lamech.Name} successfully got married.");
+}
+else
+{
+  WriteLine($"{zillah.Name} and {lamech.Name} failed to marry.");
+}
+
+lamech.OutputSpouses();
+adah.OutputSpouses();
+zillah.OutputSpouses();
+```
+
+The output should look like this:
+```
+Zillah and Lamech successfully got married.
+Lamech is married to 2 people:
+  Adah
+  Zillah
+Adah is married to 1 person:
+  Lamech
+Zillah is married to 1 person:
+  Lamech
+```
+
 # Page 237 - Implementing functionality using methods
 
 > Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 5 March 2023](https://github.com/markjprice/cs11dotnet7/issues/35).

vs4win/Chapter05/PacktLibraryNetStandard2/PersonAutoGen.cs

@@ -74,33 +74,59 @@ public partial class Person
     }
   }
 
-  private bool married = false;
+  // Is this person married to anyone?
-  public bool Married => married;
+  public bool Married => Spouses.Any();
 
-  private Person? spouse = null;
+  // Allow multiple spouses.
-  public Person? Spouse => spouse;
+  public List<Person> Spouses = new();
 
   // static method to marry
   public static void Marry(Person p1, Person p2)
   {
-    p1.Marry(p2);
+    if (p1.Spouses.Contains(p2) || p2.Spouses.Contains(p1))
+    {
+      throw new ArgumentException(
+        string.Format("{0} is already married to {1}.",
+        arg0: p1.Name, arg1: p2.Name));
+    }
+    else
+    {
+      p1.Spouses.Add(p2);
+      p2.Spouses.Add(p1);
+    }
   }
 
   // instance method to marry
   public void Marry(Person partner)
   {
-    if (married) return;
+    Marry(this, partner);
-    spouse = partner;
+  }
-    married = true;
+
-    partner.Marry(this); // this is the current object
+  public void OutputSpouses()
+  {
+    if (Married)
+    {
+      string term = Spouses.Count == 1 ? "person" : "people";
+      WriteLine($"{Name} is married to {Spouses.Count} {term}:");
+      foreach (Person spouse in Spouses)
+      {
+        WriteLine($"  {spouse.Name}");
+      }
+    }
+    else
+    {
+      WriteLine($"{Name} is not married.");
+    }
   }
 
   // static method to "multiply"
   public static Person Procreate(Person p1, Person p2)
   {
-    if (p1.Spouse != p2)
+    if (!p1.Spouses.Contains(p2))
     {
-      throw new ArgumentException("You must be married to procreate.");
+      throw new ArgumentException(
+        string.Format("{0} must be married to {1} to procreate with them.",
+        arg0: p1.Name, arg1: p2.Name));
     }
 
     Person baby = new()

vs4win/Chapter05/PeopleApp/Program.cs

@@ -211,14 +211,19 @@ Person zillah = new() { Name = "Zillah" };
 
 lamech.Marry(adah);
 // Person.Marry(zillah, lamech);
+
 if (zillah + lamech)
 {
   WriteLine($"{zillah.Name} and {lamech.Name} successfully got married.");
 }
+else
+{
+  WriteLine($"{zillah.Name} and {lamech.Name} failed to marry.");
+}
 
-WriteLine($"{lamech.Name} is married to {lamech.Spouse?.Name ?? "nobody"}");
+lamech.OutputSpouses();
-WriteLine($"{adah.Name} is married to {adah.Spouse?.Name ?? "nobody"}");
+adah.OutputSpouses();
-WriteLine($"{zillah.Name} is married to {zillah.Spouse?.Name ?? "nobody"}");
+zillah.OutputSpouses();
 
 // call instance method
 Person baby1 = lamech.ProcreateWith(adah);
@@ -248,7 +253,7 @@ for (int i = 0; i < lamech.Children.Count; i++)
 
 // Implementing functionality using local functions
 
-int number = -1; // change to -1 to make the exception handling code execute
+int number = 6; // change to -1 to make the exception handling code execute
 
 try
 {

vscode/Chapter05/PacktLibraryNetStandard2/PersonAutoGen.cs

@@ -74,33 +74,59 @@ public partial class Person
     }
   }
 
-  private bool married = false;
+  // Is this person married to anyone?
-  public bool Married => married;
+  public bool Married => Spouses.Any();
 
-  private Person? spouse = null;
+  // Allow multiple spouses.
-  public Person? Spouse => spouse;
+  public List<Person> Spouses = new();
 
   // static method to marry
   public static void Marry(Person p1, Person p2)
   {
-    p1.Marry(p2);
+    if (p1.Spouses.Contains(p2) || p2.Spouses.Contains(p1))
+    {
+      throw new ArgumentException(
+        string.Format("{0} is already married to {1}.",
+        arg0: p1.Name, arg1: p2.Name));
+    }
+    else
+    {
+      p1.Spouses.Add(p2);
+      p2.Spouses.Add(p1);
+    }
   }
 
   // instance method to marry
   public void Marry(Person partner)
   {
-    if (married) return;
+    Marry(this, partner);
-    spouse = partner;
+  }
-    married = true;
+
-    partner.Marry(this); // this is the current object
+  public void OutputSpouses()
+  {
+    if (Married)
+    {
+      string term = Spouses.Count == 1 ? "person" : "people";
+      WriteLine($"{Name} is married to {Spouses.Count} {term}:");
+      foreach (Person spouse in Spouses)
+      {
+        WriteLine($"  {spouse.Name}");
+      }
+    }
+    else
+    {
+      WriteLine($"{Name} is not married.");
+    }
   }
 
   // static method to "multiply"
   public static Person Procreate(Person p1, Person p2)
   {
-    if (p1.Spouse != p2)
+    if (!p1.Spouses.Contains(p2))
     {
-      throw new ArgumentException("You must be married to procreate.");
+      throw new ArgumentException(
+        string.Format("{0} must be married to {1} to procreate with them.",
+        arg0: p1.Name, arg1: p2.Name));
     }
 
     Person baby = new()

vscode/Chapter05/PeopleApp/Program.cs

@@ -211,14 +211,19 @@ Person zillah = new() { Name = "Zillah" };
 
 lamech.Marry(adah);
 // Person.Marry(zillah, lamech);
+
 if (zillah + lamech)
 {
   WriteLine($"{zillah.Name} and {lamech.Name} successfully got married.");
 }
+else
+{
+  WriteLine($"{zillah.Name} and {lamech.Name} failed to marry.");
+}
 
-WriteLine($"{lamech.Name} is married to {lamech.Spouse?.Name ?? "nobody"}");
+lamech.OutputSpouses();
-WriteLine($"{adah.Name} is married to {adah.Spouse?.Name ?? "nobody"}");
+adah.OutputSpouses();
-WriteLine($"{zillah.Name} is married to {zillah.Spouse?.Name ?? "nobody"}");
+zillah.OutputSpouses();
 
 // call instance method
 Person baby1 = lamech.ProcreateWith(adah);
@@ -248,7 +253,7 @@ for (int i = 0; i < lamech.Children.Count; i++)
 
 // Implementing functionality using local functions
 
-int number = -1; // change to -1 to make the exception handling code execute
+int number = 6; // change to -1 to make the exception handling code execute
 
 try
 {